The introduction last Saturday of Apple Inc.'s iPad also saw the debut of Square Inc.'s payment-card acceptance app for the mobile device.

Twitter Inc. founder Jack Dorsey announced Square in December as a payment-card acceptance device for users of Apple's iPhone but has yet to make the software available. Instead, it released a version for the iPad, a larger touch-screen device.

Square has said little publicly about its strategy, but its Web site has recently added new details.

It says merchants using the service will pay no setup or monthly fees and do not need a merchant account.

Square lists its transaction fees as 2.9% of the sale for card-present transactions and 3.5% for card-not-present transactions; it will not assess a per-transaction fee.